1. Field of the Invention
The present invention relates to piezoelectric elements which contain a specific poly(α-amino acid).
2. Discussion of the Background
The technique for producing a device on a flexible substrate by printing is called printable electronics. It is one of the next-generation key technologies, and technical development from various viewpoints has been vigorously considered in recent years. Heretofore, technical developments have been tried in driving elements, lighting elements, display elements and the like, and the realization of printing devices has come in sight. However, an appropriate material has not been found for a piezoelectric element as yet, and sufficient technical development has not been made.
A piezoelectric element is an element that converts an exerted force to voltage or a voltage to force. Heretofore, a thin film of a fluorinated polymer such as polyvinylidene fluoride (PVDF), vinylidene fluoride-trifluoroethylene copolymer (P(VDF/TrFE)) and the like has often been used for a piezoelectric element. However, a fluorinated polymer has a poor film-forming ability and causes problems in terms of uniformity of film thickness, smoothness of film surface and the like. To obtain high piezoelectricity, stretching and polarization are necessary, which problematically increases the cost and limits utilizable processes.
On the other hand, JP-A-H11-217432 discloses that a poly(α-amino acid) which takes a helix form can be used as a piezoelectric material without a special treatment. In addition, JP-A-2005-217111 proposes a polymer piezoelectric substance that can be obtained from a poly(α-amino acid).
However, JP-A-H11-217432 does not describe a poly(α-amino acid) with specifically measured piezoelectricity. In addition, the poly(α-amino acid) composed of poly-γ-benzyl-L-glutamate and/or poly-γ-methyl-L-glutamate specifically described in JP-A-H11-217432 and JP-A-2005-217111 shows insufficient piezoelectricity and can only be dissolved in specific solvents. Therefore, they cannot be used as a printable material, which is required to be soluble in various solvents and resins.